1. Field of the Invention
The present invention relates to an apparatus and a method for printing, and more particularly, to printing multi-color images onto cylindrical portions such as "can bodies" of so-called two-piece cans and the like. More specifically, the present invention relates to a multi-color printing apparatus and a multi-color printing method capable of easily conveying out multi-color printing onto vessels, such as beverage cans, which permit a wide variety of fine colorings by overlapping images at a high velocity.
2. Discussion of Background
Offset flexographic printing apparatuses have been used as conventional printing apparatuses for decorating the can body of two-piece cans and the like. Essentially, all the colors applied to the can body, so as to create distinctive decorations or images thereon, are applied by a single ink transfer blanket. Then, the can makes one complete revolution with respect to the ink transfer blanket to achieve perfect decoration, as intended.
The respective colors for defining an entire image are positioned before they are applied to the surface of the can body. The ink applied to the ink transfer blanket is wet ink, where wet ink of one color is located adjacent to wet ink of a second color. This may result in phenomena known in the can decoration industry as "back trapping," where one ink color runs into the adjacent color. As a result, the resolution of the ink, or quality of graphics decoration, is inherently limited with the conventional offset flexographic printing process.
There is also known a multi-color printing apparatus composed of a plurality of ink transfer blanket cylinders arranged in a seriatim (serial) array and a can carrier that is moved to position cans at successive printing stations where the blanket cylinders are located. At the printing stations, the blanket cylinders and the cans are rotated while they are in contact with each other so as to transfer ink onto the cans. Different ink colors are used at each of a plurality of printing stations to provide multi-color image printing on cans in diverse and highly artistic patterns.
In the above multi-color printing apparatus, the cans can be moved on a carrier by the use of a transport belt where the blanket array is in a linear arrangement.
A coating unit can be used following ink printing to overlay a finish coat such as a varnish onto the printed image. In the apparatus, each blanket is located at an associated printing station and each printing station includes an associated source for supplying ink to the blanket. Further, there is also provided at least one ink dryer.
The carrier is movable so as to sequentially position the subject can at successive printing stations and cause the can to come into contact with the ink transfer blanket so that the ink is applied to the outer surface of the can. In addition, the ink drier is located so as to dry the ink, applied to the can at a printing station, before the can is positioned at the next printing station.
As recognized by the present inventors, the above described conventional printing apparatus and method still have the following problems. Generally, it is desired to shorten the entire printing process time because the inks of the respective colors must be individually dried to prevent the aforementioned back trapping, and thus, a long time is needed to finish the printing of all the colors. It is also desirable to maintain the accurate alignment of the can body throughout a plurality of individually located ink printing stations and ink curing or drying stations interposed between the respective stations to correctly print the respective colors. Further, as appreciated by the present inventors, it is desirable to print a photograph or a complex image having an image quality comparable to a photograph whose printing has been conventionally difficult.